1. Field of the Invention
The present invention relates generally to networking computer systems, and more particularly to networking computer systems having devices that emulate a single router in a switch stack.
2. Background Information
A virtual local area network (VLAN) is a group of personal computers (PCs), servers, and other network resources and stations that behave as if they were connected to a single network segment, as determined by some network administrator-defined criteria. For example, all marketing personnel may be spread throughout a building, but if they are all assigned to a single VLAN, they can share resources and bandwidth as if they were connected to the same segment.
FIG. 1 illustrates an example of a building 10 having one or more VLANs. The VLANs are segmented from each other by one or more switches 14, 16, 18 operating at the Media Access Control (MAC) sublayer of the Data Link layer (Layer 2) of the International Standards Organization (ISO) Open Systems Interconnection (OSI) reference model. For instance, one of the VLANs can comprise PCs 19 associated with an administrative department. Other VLANs can comprise PCs 20 associated with a marketing department and PCs 21 associated with an engineering department. Each of these VLANs can further include one or more, shared or non-shared, printers 22, hubs 24, and servers 26. The switches 14, 16, 18 are in turn coupled to a router 28 operating at the Network layer (Layer 3) of the OSI reference model. The router 28 connects the VLANs together or connects the VLANs to a wide area network (WAN) 30, and allows communication between the various VLANs or between the VLANs and the WAN 30. The various components (e.g., the PCs 19, 20, 21) connected together in an individual VLAN are sometimes referred to as “nodes” or “stations.” The switches 14, 16, 18 and the router 28 are sometimes referred to as “routing devices” (RDs).
In operation, messages (e.g., packets) transferred between nodes of the same VLAN are transmitted at the MAC sublayer (Layer 2), based on each node's MAC address (e.g., by using MAC source and destination addresses). Messages transferred between nodes of different VLANs are most often transferred at the Network layer (Layer 3) via the router 28, based on a Network layer address, such as an Internet Protocol (IP) address of each node.
In an effort to increase network capacity and performance, RDs (e.g., any one of the switches 14, 16, 18 that have Layer 3 switching capability) and non-routing devices (NRDs) (e.g., any one of the switches 14, 16, 18 that have only Layer 2 switching capability, Gigabit modules for Gigabit Ethernet applications, or asynchronous transfer mode (ATM) modules) are sometimes connected in a “switch stack” configuration. As shown in FIG. 2, a switch stack 32 may comprise a plurality of stack devices 34, 36, 38, 40, 42, which can be RDs or NRDs. Each stack device 3442 can work as both a stand-alone unit or as a unit belonging to part of the stack 32. Further, each stack device 34–42 in the stack 32 can “see” all of the other stack devices 34–42 in the stack 32 as a “neighbor.” That is, the stack devices 34–42 are joined together via their stack ports (not shown) to form a matrix connection 44 in a backplane 46. The stack devices 34–42 have a plurality of front ports 48 connected to nodes of their respective VLANs.
Referring next to FIG. 3, a RD (e.g., the stack device 34) performs routing between VLANs A and B with corresponding router interfaces 50 and 52, for each VLAN A and B, respectively. Each router interface 50, 52 has a MAC address (e.g., MAC A and MAC B addresses) associated with it, which is used by the router 28 (see, e.g., FIG. 1) when transmitting packets, and packets sent to that MAC address are sent to the router 28. The router 28 can also receive other packets depending on the types of higher layer protocols (e.g., Layer 3 or Layer 4 protocols like IP Routing Information Protocol (IP RIP), IP filtering, Resource Reservation Setup Protocol (RSVP), IP multicast, Internet Group Multicast Protocol (IGMP) pruning, and Internet Packet Exchange RIP or Service Access Protocol (IPX RIP/SAP)) that are implemented when broadcast or multicast packets are sent between the VLANs. As such, the router interfaces 50, 52 are also associated with IP and IPX addresses, as shown in FIG. 3.
However, configurations such as those shown in FIGS. 2 and 3 suffer from several drawbacks. For instance, although the stack devices 34–42 are stacked, they are managed as individual devices, and therefore add to the number of devices for which a network administrator is responsible. Further, inter-switch connections of the switch stack 32 limit their scalability. For example, to obtain scalable performance for the five stack devices 34–42 shown in FIG. 2, routing needs to be configured in each of the devices 34–42 and up to five different IP or IPX addresses need to be used for each VLAN A and B. This type of configuration would require complicated analysis as well as reconfiguration of the total network in order to obtain proper loadsharing. Accordingly, how RDs and NRDs are stacked together needs improvement.